Silver halide diffusion process and products therefor



March 28, 1967 FOSTER ET AL 3,311,473

SILVER HALIDE DIFFUSION PROCESS AND PRODUCTS THEREFOR Filed June 28. 1962 EXPOSURE LWage 1 13 JSILVER HAUDE-GELAT/N LAYER 1:1- =-':i:-ji 5- j ,f \SILVER PREC/PlTAT/NG LAYER I 0 I {I IJ-SUPP0RT 1 DEVELOPMENT, DIFFUSION TRANSFER OF RESIDUAL SILVER HAUDE AND REMOVAL OF EMULSION LAYER fi'figez Donald]? Foster Edward C.Yackel IN V EN TORJ United States l atent O 3,311,473 SILVER HALIDE DIFFUSION PRGCESS AND PRODUCTS THEREFOR Donald P. Foster and Edward C. Yackel, Rochester, N.Y., assignors to Eastman Kodak Company, Rochester, N.Y., a corporation of New Jersey Filed June 28, 1962, Ser. No. 205,995 12 Claims. (Cl. 96-29) This invention relates to a photographic process of the silver halide diffusion transfer type wherein undeveloped silver halide of an emulsion layer is transferred as a silver complex imagewise by diffusion to a silver precipitating or nucleating layer generally to form a silver photographic image, generally a positive, therein.

As is known in the art, the diffusion transfer type process can be carried out by developing an exposed emulsion layer with a developing solution containing a silver halide solvent after which the emulsion layer is placed into contact with a second element carrying a silver precipitating layer to cause the undeveloped silver halide to transfer imagewise as a silver complex to the second element and form an image thereon.

The diffusion transfer process has also been carried out utilizing a multilayer element such as one carrying on a support two gelatin layers of different solubility, for

example, the layer next to the support containing a silver.

precipitating agent and being harder than the outer gelatin layer which is a gelatin emulsion layer containing silver halide. After exposure of the element, development is carried out with the silver halide solvent containing developer to obtain a silver positive in the hardened gelatin silver precipitating layer, after which the emulsion layer containing the negative silver image is washed or stripped 06, leaving the positive image on the support.

As a practical matter, it is difiicult to harden the underlying gelatin nucleating layer of an element of this type without unduly hardening the outer gelatin emulsion layer and, even then, over a period of time, the silver halide emulsion layer tends to harden which makes the differential removal in the final step of the process difficult or impossible.

We have discovered a method of keeping the unhardened gelatin from becoming insoluble when coated over hardened gelatin while not affecting the hardness of the hardened layer.

One object of the invention is to provide an all-gel system for a two-layer diffusion transfer process having an unhardened gelatin, silver-halide containing layer which resists hardening coated over a hardened gel, silver precipitating layer.

An additional object is to provide keeps unhardened gel from becoming insoluble in the presence of gel hardening agents, such as formaldehyde. An additional object is to provide a gel layer which can easily be removed by washing away with water.

The above objects are attained by adding semicarbazide salt to the unhardened gelatin layer which is coated over the hardened gel layer. The semicarbazide is added in an amount of 3 to 16% by weight based on the gelatin content.

In the accompanying drawing is illustrated, in greatly enlarged cross-sectional view, a sensitive element illustrating one embodiment of our invention. As shown therein, in stage 1, a representative sensitive element includes a support 10, such as paper, cellulose ester or synthetic resin, if desired carrying a subbing layer not shown, and on the support the silver precipitating layer 11, for example, a gelatin layer containing a colloidal heavy metal or heavy metal sulfide and thereon an emulsion layer 12 containing silver halide grains dispersed in gelatin containing semicarbazide. As shown in stage 1,

an agent which ice the element is exposed to a light, halftone or continuous tone subject in a suitable manner, preferably so as to obtain a right-reading reproduction, the exposure being shown as taking place in area 13 of the emulsion layer 12.

In carrying out the process of our invention, the exposed element is then developed with a silver halide developing solution containing a silver halide solvent, such as sodium thiosulfate, with the result that a silver image is developed in area 13 and shortly thereafter the residual undeveloped silver halide is transformed to a soluble silver complex, a portion of which diffuses imagewise to a silver precipitating layer 11, where an argental image is formed by reaction of the silver complex with the silver precipitating agent of the silver precipitating layer. The emulsion layer 12 containing the negative silver image is then merely washed free from the support with an excess of water to obtain the reproduction shown in stage 2 of the drawing wherein the argental positive image occupies areas 14 of the silver precipitating layer 11.

The silver precipitating layer or stratum referred to herein is a water-permeable, organic colloid layer, preferably gelatin, containing a silver precipitating agent; that is, an agent capable of yielding with silver ion a darkcolored argental or silver-containing substance, when dissolved silver salts from the emulsion layer come into contact with it. The silver precipitating agent may comprise either physical development nuclei or a chemical precipitant for silver ions.

Suitable silver precipitating agents for use in the silver precipitating layer for forming the argental image include sulfides, selenides, polysulfides, polyselenides, thiourea, mercaptans, stannous halides, heavy metals and heavy metal salts, and fogged silver halide. Heavy metal sulfides such as lead, silver, zinc, antimony, cadmium and bismuth sulfides are useful, particularly the sulfides of lead and zinc alone or in admixture, or complex salts of these with thioacetamide, dithiol-oxamide, or dithiolbiuret. The heavy metals include silver, gold, platinum, palladium and mercury, preferably in the colloidal form. The noble metals are particularly eflicacious.

The silver precipitating agents may be applied directly to a support, such as paper, or to suitable subbed cellulose derivative supports, or synthetic polymer supports, from solutions or dispersions of the silver precipitating agents in colloidal vehicles, such as gelatin. The gelatin can be hardened using hardeners known in the art, such as formaldehyde, chromic chloride, muchloric acid, diketones (bis-acetyl), or the like. In general, the aldehyde-type hardeners are preferred. When a gelatin substitute is used, the colloidal vehicle must be hardened or else must be rendered insoluble in the wash solution used to remove the unhardened gelatin layer from the surface.

The silver halide gelatino emulsion can be applied directly over the silver precipitating layer, but a thin layer of gelatin or an alkaline-soluble polymeric material sufficiently sensitive to salts so that solution does not occur during processing but occurs as soon as water is applied as in washing may be first applied, followed 'by the emulsion layer. This thin layer is not essential; however, it has been found to facilitate the clean removal of the emulsion from the silver precipitating layer.

The silver halide component of the photographic emulsion is not especially critical and can include various silver halides and mixtures of silver halide, such as silver bromoiodide, silver chloride or silver bromide, etc. They may be optically sensitized in the usual manner.

The emulsion may be developing-out emulsions, designed for development to negative images in which case the image obtained in the silver precipitating layer is a positive with respect to the original subject. If desired, the emulsion can be of the direct positive type, with the result that the silver image developed in the emulsion is a positive and the image in the silver precipitating layer a negative in respect to the original subject. The procedures of Leermakers, U.S. Patent No. 2,184,013, and Kendal et al., US. Patent No. 2,541,472, are useful in conferring the direct positive characters to the emulsions.

The silver halide developing solution used for initiating the development of the exposed sensitive element described above is not especially critical and can be of the conventional type used for developing film or papers with the exception that a silver halide solvent such as sodium thiosulfate, sodium thiocyanate, etc., is present in the quantity required to form the soluble silver complex, which diffuses imagewise to the silver precipitating layer. Silver halide developing agents useful in the developing solution include hydroquinones, e.g. halogenated hydroquinones, toluhydroquinones, aminophenols, e.g. monomethyl-p-arninophenol sulfate and glycerine, 3-pyrazolidone developing agents, such as l-phenyl-S-pyrazolidone, such as combinations of 1-phenyl-3-pyrazolidones with hydroquinones, ascorbic acid, reductones, and the like, may be used.

Yackel et al., US. Patent No. 3,020,155, issued February 6, 1962, discloses a photographic diffusion transfer process in which a silver halide emulsion in a vehicle of alkali-soluble cellulose derivative is used to obviate hardening from in the emulsion layer. It will be appreciated that modifications disclosed in connection with Yackel et al. product, such as improving the tone of the image, and the like, may also be used in connection with our invention.

In the Yackel et a1. process and the process of the present invention in the examples hereinafter, the silver halide developing agent may be incorporated in either the developing solution or the emulsion itself. In the latter case, it is preferable to use a substantially nondiffusing developing agent, such as 3,4-dihydroxydiphenyl, in the emulsion layer.

The following examples illustrate our invention, ,but are not intended to limit it in any way.

Example I A coating was prepared which contained 0.270 g. gelatin, 16 micrograms zinc sulfide, and 0.018 g. formaldehyde per square foot of film base. Over this was coated a silver halide gelatino sensitized emulsion at a coverage to yield .625 g. gelatin, 0.360 g. silver, and 0.050 g. semicarbazide HCl-sodium salt. Evaluation was carried out by processing, after exposure, in a developer con taining the following:

Water to make 1 liter.

With fresh samples of the above coating and a control coating without the semicarhazide, the negative top layer could be washed off easily. After four weeks incubation at 120 F., 50% relative humidity, however, the negative layer of the control could not be removed, whereas the negative layer of the coating containing the semicarbazide salt could be readily removed.

The semicarbazide salt can be incorporated in a barrier layer between the nuclei and emulson layers if such a barrier layer is used. The semicarbazide salt can be placed in a wateror alkali-permeable layer where it will be readily available to the emulsion layer to prevent hardening of this layer from migration of the hardener from the nuclei layer. The semicarbazide salt might be placed instead in a permeable overcoat over the emulsion layer where it would be free to diffuse into the emulsion layer to inhibit hardening therein.

Example 2 A coating was prepared which contained 0.270 g. gelatin, 1.6 l0 g. nickel sulfide, and 0.018 g. formaldehyde per square foot of film base. Samples of this coating were over coated with a sensitized gelatino-silver halide emulsion at a coverage to yield 0.530 g. gelatin, 0.360 g. silver and the level of semicarbazide salt listed below.

Coating A--.033 g. semicarbazide-HCl-sodium salt per sq. ft.

Coating B.050 g. semicarbazide-HCl-sodium salt per sq. ft.

Coating C.067 g. semicarbazide-HCl-sodium salt per sq. ft.

These samples were evaluated as described in Example 1 and were all found to yield the useful results described for the experimental coating described in Example 1.

The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention as described hereinabove and as defined in the appended claims.

We claim:

1. A light-sensitive photographic element comprising a support, a silver precipitating stratum containing silver precipitating nuclei and hardened colloid on the support, said colloid hardened with an aldehyde type hardener, and adhered to said stratum an unhardened light-sensitive gelatin emulsion layer containing silver halide and a compound selected from the class consisting of semicarbazide and the water-soluble semicarbazide salts thereof.

. 2. A light-sensitive photographic element comprising a support, a silver precipitating stratum containing silver precipitating nuclei and hardened colloid on the support, said colloid hardened with an aldehyde type hardener, and adhered to said stratum and unhardened light-sensitive gelatin emulsion layer containing silver halide and 316% by weight semicarbazide, based on the gelatin in the emulsion.

3. A method of forming a photographic image which comprises developing an exposed silver halide emulsion comprising the top layer in a photographic element including a support, a silver precipitating stratum containmg silver precipitating nuclei and hardened colloid on the support, said colloid hardened with an aldehyde type hardener and adhered to said stratum an unhardened light-sensitive gelatino-silver halide emulsion layer containing silver halide and a compound selected from the class consisting of semicarbazide and the water-soluble semicarbazide salts thereof, by developing a latent image in the emulsion layer with a silver halide developing solution containing a silver halide developing agent and a silver halide solvent for a time sufficient to form a silver image and an imagewise distribution of a soluble silver complex in the emulsion layer, allowing a portion of said silver complex to diffuse imagewise to said silver precipitating stratum and the silver of said portion of said silver complex to he precipitated in said stratum and removing the emulsion layer from said stratum.

4. A light-sensitive photographic element comprising a support, a silver precipitating stratum containing silver precipitating nuclei and hardened colloid on the support, said colloid hardened with an aldehyde type hardener and adhered to said stratum an unhardened light-sensitive gelatin emulsion layer containing silver halide and semicarbazide hydrochloride-sodium salt. I

5. A light-sensitive photographic element comprising a support, a silver precipitating stratum containing silver precipitating nuclei and hardened colloid on the support, said colloid hardened with an aldehyde type hardener, and adhered to said stratum an unhardened light-sensitive gelatin emulsion layer containing silver halide and 316% by weight semicarbazide hydrochloride-sodium salt, based on the gelatin in the emulsion.

6. A method of forming a photographic image which comprises developing an exposed silver halide emulsion comprising the top layer in a photographic element including a support, a silver precipitating stratum containing silver precipitating nuclei and hardened colloid on the support, said colloid hardened with an aldehyde type hardener, and adhered to said stratum an unhardened light-sensitive gelatino-silver halide emulsion layer containing silver halide and semicarbazide hydrochloridesodium salt, by developing a latent image in the emulsion layer with a silver halide developing solution containing a silver halide developing agent and a silver halide solvent for a time sufiicient to form a silver image and an imagewise distribution of a soluble silver complex in the emulsion layer, allowing a portion of said silver complex to diffuse imagewise to said silver precipitating stratum and the silver of said portion of said silver complex to be precipitated in said stratum and removing the emulsion layer from said stratum.

7. A light-sensitive photographic element comprising a support, a silver precipitating stratum containing silver precipitating nuclei and hardened colloid on the support, said colloid hardened with an aldehyde type hardener, a colloid barrier layer on said stratum containing a compound selected from the class consisting of semicarbazide and the water-soluble semicarbazide salts thereof and adhered to said barrier layer an unhardened light-sensitive gelatin emulsion layer containing silver halide.

8. A light-sensitive photographic element comprising a support, a silver precipitating stratum containing silver precipitating nuclei and hardened colloid on the support, said colloid hardened with an aldehyde type hardner, a colloid barrier layer on said stratum containing 316% by weight of a compound selected from the class consisting of semicarbazide and the Water-soluble semicarbazide salts thereof, and adhered to said barrier layer an unhardened light-sensitive gelatin emulsion layer containing silver halide.

9. A method of forming a photographic image which comprises developing an exposed silver halide emulsion comprising the top layer in a photographic element including a support, a silver precipitating stratum containing silver precipitating nuclei and hardened colloid on the support, said colloid hardened with an aldehyde type hardener, a colloid barrier layer on said stratum containing a compound selected from the class consisting of semicarbazide and the water-soluble semicarbazide salts capable of reacting with an aldehyde to form semicarbazones, and adhered to said barrier layer an unhardened light-sensitive gelatino-silver halide emulsion layer containing silver halide and a compound selected from the class consisting of semicarbazide and the water-soluble semicarbazide salts thereof, by developing a latent image in the emulsion layer with a silver halide developing solution containing a silver halide developing agent and a silver halide solvent for a time suflicient to form a silver 10. A light-sensitive photographic element comprisinga support, a silver precipitating stratum containing silver precipitating nuclei and hardened colloid on the support, said colloid hardened with an aldehyde type hardener, a colloid barrier layer on said stratum containing semicarbazide.

11. A light-sensitive photographic element comprising a a support, a silver precipitating stratum containing silver precipitating nuclei and hardened colloid on the support, said colloid hardened with an aldehyde type hardener, a colloid barrier layer on said stratum containing 316% by weight of a semicarbazide and adhered to said barrier layer an unhardened light-sensitive gelatin emulsion layer containing silver halide.

12. A method of forming a photographic image which comprises developing an exposed silver halide emulsion comprising the top layer in a photographic element including a support, a silver precipitating stratum containing silver precipitating nuclei and hardened colloid on the support, said colloid hardened with an aldehyde type hardener, a colloid barrier layer on said stratum containing a semicarbazide, and adhered to said barrier layer an unhardened light-sensitive gelatino-silver halide emulsion layer containing silver halide and a compound selected from the class consisting of semicarbazide and the watersoluble semicarbazide salts thereof, by developing a latent image in the emulsion layer with a silver halide developing solution containing a silver halide developing agent and a silver halide solvent for a time suflicient to form a silver image and an imagewise distribution of a soluble silver complex in the emulsion layer, allowing a portion of said silver complex to diifuse imagewise to said silver precipitating stratum and the silver of said portion of said silver complex to :be precipitated in said stratum and removing the emulsion layer from said stratum.

References Cited by the Examiner UNITED STATES PATENTS OTHER REFERENCES Mees: Theory of the Photographic Process, Macmillan, NY. (1954), pp. 541-544.

Noller: Chemistry of Organic Compounds, 2nd edition Saunders, Philadelphia (1957), p. 211.

NORMAN G. TORCHIN, Primary Examiner. G. H. BJORGE, Assistant Examiner. 

1. A LIGHT-SENSITIVE PHOTOGRAPHIC ELEMENT COMPRISING A SUPPORT, A SILVER PRECIPITATING STRATUM CONTAINING SILVER PRECIPITATING NUCLEI AND HARDENED COLLOID ON THE SUPPORT, SAID COLLOID HARDENED WITH AN ALDEHYDE TYPE HARDENER, AND ADHERED TO SAID STRATUM AN UNHARDENED LIGHT-SENSITIVE GELATIN EMULSION LAYER CONTAINING SILVER HALIDE AND A COMPOUND SELECTED FROM THE CLASS CONSISTING OF SEMICARBAZIDE AND THE WATER-SOLUBLE SEMICARBAZIDE SALTS THEREOF.
 7. A LIGHT-SENSITIVE PHOTOGRAPHIC ELEMENT COMPRISING A SUPPORT, A SILVER PRECIPITATING STRATUM CONTAINING SILVER PRECIPITATING NUCLEI AND HARDENED COLLOID ON THE SUPPORT, SAID COLLOID HARDENED WITH AN ALDEHYDE TYPE HARDENER, A COLLOID BARRIER LAYER ON SAID STRATUM CONTAINING A COMPOUND SELECTED FROM THE CLASS CONSISTING OF SEMICARBAZIDE AND THE WATER-SOLUBLE SEMICARBAZIDE SALTS THEREOF AND ADHERED TO SAID BARRIER LAYER AN UNHARDENED LIGHT-SENSITIVE GELATIN EMULSION LAYER CONTAINING SILVER HALIDE. 